Intervertebral disc nucleus implants and methods

ABSTRACT

Nucleus pulposus implants that are resistant to migration in and/or expulsion from an intervertebral disc space are provided. In one form of the invention, an implant includes a load bearing elastic body surrounded in the disc space by an anchoring, preferably resorbable, outer shell. In certain forms of the invention, the elastic body is surrounded by a supporting member, such as a band or jacket, and the supporting member is surrounded by the outer shell. Kits for forming such implants are also provided. In another form of the invention, an implant is provided that has locking features and optional shape memory characteristics. In yet another aspect of the invention, nucleus pulposus implants are provided that have shape memory characteristics and are configured to allow short-term manual, or other deformation without permanent deformation, cracks, tears, breakage or other damage. Methods of forming and implanting the implants are also described.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to nucleus pulposus implants andmethods for their implantation.

[0002] The intervertebral disc functions to stabilize the spine and todistribute forces between vertebral bodies. A normal disc includes agelatinous nucleus pulposus, an annulus fibrosis and two vertebral endplates. The nucleus pulposus is surrounded and confined by the annulusfibrosis.

[0003] Intervertebral discs may be displaced or damaged due to trauma ordisease. Disruption of the annulus fibrosis may allow the nucleuspulposus to protrude into the vertebral canal, a condition commonlyreferred to as a herniated or ruptured disc. The extruded nucleuspulposus may press on a spinal nerve, which may result in nerve damage,pain, numbness, muscle weakness and paralysis. Intervertebral discs mayalso deteriorate due to the normal aging process. As a disc dehydratesand hardens, the disc space height will be reduced, leading toinstability of the spine, decreased mobility and pain.

[0004] One way to relieve the symptoms of these conditions is bysurgical removal of a portion or all of the intervertebral disc. Theremoval of the damaged or unhealthy disc may allow the disc space tocollapse, which would lead to instability of the spine, abnormal jointmechanics, nerve damage, as well as severe pain. Therefore, afterremoval of the disc, adjacent vertebrae are typically fused to preservethe disc space. Several devices exist to fill an intervertebral spacefollowing removal of all or part of the intervertebral disc in order toprevent disc space collapse and to promote fusion of adjacent vertebraesurrounding the disc space. Even though a certain degree of success withthese devices has been achieved, full motion is typically never regainedafter such vertebral fusions. Attempts to overcome these problems haveled to the development of disc replacements. Many of these devices arecomplicated, bulky and made of a combination of metallic and elastomericcomponents. Thus, such devices require invasive surgical procedures andtypically never fully return the full range of motion desired.

[0005] More recently, efforts have been directed to replacing thenucleus pulposus of the disc with a similar gelatinous material, such asa hydrogel. However, there exists a possibility of tearing or otherwisedamaging the hydrogel implant during implantation. Moreover, oncepositioned in the disc space, many hydrogel implants may migrate in thedisc space and/or may be expelled from the disc space through an annulardefect, or other annular opening. A need therefore exists for moredurable implants, as well as implants that are resistant to migrationand/or expulsion through an opening in the annulus fibrosis. The presentinvention addresses these needs.

SUMMARY OF THE INVENTION

[0006] Nucleus pulposus implants that are resistant to migration inand/or expulsion from an intervertebral disc space are provided.Accordingly, in one aspect of the invention, nucleus pulposus implantsare provided that include a load bearing elastic body sized forintroduction into an intervertebral disc space and surrounded by aresorbable shell that provides the initial fixation for the elastic bodywithin the disc space. The implant may include various surface featureson its outer surface, including surface configurations or chemicalmodifications, that enhance the bonding between the outer surface of theimplants and the resorbable shell. Kits for forming such implants arealso provided. In other forms of the invention, the elastic body may besurrounded by a supporting member wherein the supporting member issurrounded by the resorbable shell.

[0007] In yet another aspect of the invention, nucleus pulposus implantsare provided that have shape memory and are configured to allowextensive short-term deformation without permanent deformation, crackstears or other breakage. In one form of the invention, an implantincludes a load bearing elastic body sized for placement into anintervertebral disc space. The body includes a first end, a second endand a central portion wherein the first end and second end arepositioned, in a folded, relaxed configuration, adjacent to the centralportion to form at least one inner fold. The inner fold preferablydefines an aperture. The elastic body is deformable into a second,straightened, non-relaxed configuration for insertion through an openingin an intervertebral disc annulus fibrosis. The elastic body isdeformable automatically back into a folded configuration after beingplaced in the intervertebral disc space. Advantageously, where theimplant having shape memory is formed of a hydrogel material, or otherhydrophilic material that may be dehydrated, the implant may be fully orpartially dehydrated prior to insertion such that it may be insertedthrough a relatively small opening in the annulus fibrosis. The openingmay, for example, be a pre-existing defect or may be made by making asmall incision.

[0008] In still other aspects of the invention, nucleus pulposusimplants having locking features and optionally having shape memory areprovided. In one embodiment, an implant includes a load bearing elasticbody having a first end and a second end that are configured for matingengagement with each other. The implant has a first, lockedconfiguration wherein the first and second ends are matingly engaged toeach other. The implant may be configured into a second, straightenedconfiguration by application of external force for insertion through anopening in an intervertebral disc annulus fibrosis. When the implantincludes shape memory characteristics, it may be automaticallyconfigured, or otherwise returned, back into its first, lockedconfiguration after insertion through the opening in the annulusfibrosis and after any external force is removed, or may be placed intoits locked configuration by application of external force.

[0009] In other aspects of the invention, methods of implanting thenucleus pulposus implants of the present invention are provided. In onemode of carrying out the invention, a method includes providing theappropriate implant, preparing the intervertebral disc space to receivethe implant and then placing the implant into the intervertebral discspace. Where the implant includes a load bearing elastic body and anouter resorbable shell, a preferred method includes preparing theintervertebral disc space to receive the implant, introducing theelastic body forming the core of the implant into the disc space whereinthe body is surrounded in the disc space by a resorbable outer shell.The material forming the resorbable shell may be placed in the discspace prior to, after, or at the same time as insertion of the elasticbody. Alternatively, the elastic body may be surrounded by the outershell prior to introduction of the elastic body into the intervertebraldisc space.

[0010] It is an object of the invention to provide nucleus pulposusimplants, and kits for their formation, that are resistant to migrationin and/or explusion from an intervertebral disc space.

[0011] It is a further object of the invention to provide nucleuspulposus implants having shape memory that are configured to allowextensive short term manual, or other deformation without permanentdeformation, cracks, tears, breakage or other damage.

[0012] It is yet another object of the present invention to providenucleus pulposus implants having locking features.

[0013] It is a further object of the present invention to providemethods of forming and implanting the nucleus pulposus implantsdescribed herein.

[0014] These and other objects and advantages of the present inventionwill be apparent from the description herein.

BRIEF DESCRIPTION OF THE FIGURES

[0015]FIG. 1 depicts a side view of a cross-section of a nucleuspulposus implant, including an elastic body 15 surrounded by ananchoring outer shell 30, implanted in the intervertebral disc space ofa disc.

[0016]FIG. 2 depicts a top, cross-sectional view of the nucleus pulposusimplant of FIG. 1.

[0017]FIG. 3 depicts a side view of a cross-section of the nucleuspulposus implant of FIG. 1 after outer shell 30 has been resorbed andreplaced by fibrous scar tissue 33.

[0018]FIG. 4 shows a top, cross-sectional view of the nucleus pulposusimplant of FIG. 3.

[0019]FIG. 5 shows a side view of a cross-section of a nucleus pulposusimplant, including an elastic body 15 surrounded by a supporting member34, in the form of a band, wherein the supporting member is surroundedby an anchoring outer shell 30, implanted in the intervertebral discspace of a disc.

[0020]FIG. 6 depicts a side view of a cross-section of a nucleuspulposus implant, including an elastic body 15 surrounded by asupporting member 37, in the form of a jacket, wherein the supportingmember is surrounded by an anchoring outer shell 30, implanted in theintervertebral disc space of a disc.

[0021] FIGS. 7A-7D depict various patterns of a supporting member of thepresent invention.

[0022]FIG. 8 depicts a side view of a cross-section of a nucleuspulposus implant including an elastic body 15 surrounded by a supportingmember 34, taking the form of a band, that is further reinforced, orotherwise supported, by straps 420 and 430. The implant is surrounded byan anchoring outer shell 30 and is shown implanted in the intervertebraldisc space of a disc.

[0023]FIG. 9 shows a top, cross-sectional view of the nucleus pulposusimplant of FIG. 8.

[0024]FIG. 10 depicts a side view of an alternative embodiment of anucleus pulposus implant of the present invention that includesperipheral supporting band 34″ and securing straps 520, 530, 540 and 550and is surrounded by an anchoring outer shell 30 and implanted in theintervertebral disc space of a disc.

[0025]FIG. 11 depicts a top, cross-sectional view of the nucleuspulposus implant of FIG. 10.

[0026]FIG. 12 depicts a top view of an alternative embodiment of anucleus pulposus implant having shape memory.

[0027]FIG. 13 shows a side view of the implant shown in FIG. 12.

[0028] FIGS. 14A-14J depict portions of nucleus pulposus implants withsurface modifications. FIGS. 14A-14H show side views of top portions ofthe implants, and FIG. 141 and FIG. 14J show top views of the viewsshown in 14C and 14D, respectively.

[0029] FIGS. 15A-15N show top views of alternative embodiments ofnucleus pulposus implants having shape memory in folded, relaxedconfigurations.

[0030] FIGS. 16A-16N depict top views of the implants shown in FIGS.15A-15N, respectively, in unfolded, non-relaxed configurations.

[0031]FIG. 17 depicts a top view of an alternative embodiment of anucleus pulposus implant of the present invention having a self-lockingfeature. The implant is shown in its locked, relaxed configuration.

[0032]FIG. 18 depicts a side view of the implant of FIG. 17.

[0033]FIG. 19 depicts a side view of the implant of FIG. 18 in anunfolded, non-locked, non-relaxed configuration.

[0034]FIG. 20 depicts one step in a method of implanting nucleuspulposus implant 40 into intervertebral disc space 20 between vertebrae21 and 22 using a conventional implantation tool 310.

[0035]FIG. 21 depicts a top, cross-sectional view of a nucleus pulposusimplant 10 in its folded, relaxed configuration positioned inintervertebral disc space 20.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to preferred embodimentsand specific language will be used to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications of the invention, and such further applications of theprinciples of the invention as illustrated herein, being contemplated aswould normally occur to one skilled in the art to which the inventionrelates.

[0037] The present invention provides prosthetic intervertebral discnucleus pulposus implants that may fully or partially replace thenatural, or native, nucleus pulposus in mammals, including humans andother animals. In one aspect of the invention, implants are providedthat are configured to resist expulsion or other migration through adefect, or other opening, in the annulus fibrosis and to resistexcessive migration within an intervertebral disc space. In certainforms, these implants combine the advantages of an injectable/in-situcuring implant with a pre-formed implant. For example, a nucleuspulposus implant may include a load bearing elastic body surrounded byan outer, preferably resorbable or otherwise temporary, shell. The outershell advantageously anchors the elastic body within the intervertebraldisc space. The surface of the elastic body may include various surfacefeatures, including various macro-surface patterns, and chemical orphysical modifications as described herein to further enhance fixationof the implant to the outer resorbable shell. The surface features, suchas the macro-surface patterns and physical modifications, for example,are also expected to enhance fixation of the elastic body to surroundingtissue such that, in certain forms of the invention, no outer-shell maybe needed.

[0038] In other aspects of the invention, nucleus pulposus implantshaving shape memory that are configured to allow extensive short-termmanual or other deformation without permanent deformation, cracks,tears, breakage or other damage are provided. In preferred forms of theinvention wherein the implants are formed from a hydrogel or otherhydrophilic material, the implants can not only pass through arelatively small incision in the annulus fibrosis, but can alsosubstantially fill and conform to the intervertebral disc space. In oneform of the invention, an implant includes a load bearing elastic bodywith shape memory having first and second ends that are positionedadjacent to a central portion to form at least one inner fold. The innerfold desirably defines an aperture.

[0039] In other embodiments of the invention, the shape memory implantsare configured to form a spiral or other annular shape in the discspace, and may also be configured to have ends that matingly engage eachother for further securing the implant in the disc cavity. Methods ofmaking and implanting the implants described herein are also provided.

[0040] As disclosed above, in a first aspect of the invention, a nucleuspulposus implant is provided that includes a load bearing elastic bodysized for introduction into an intervertebral disc space and surroundedby an outer, preferably resorbable, shell. Referring now to FIGS. 1 and2, prosthetic implant 10 includes a core load bearing elastic body 15disposed in intervertebral disc space 20, between vertebral body 21 and22 and surrounded by an outer shell 30. More specifically, elastic body15 has an outer surface 16 in contact with, and preferably bonded to, anouter shell 30 that may advantageously be resorbable, or otherwisetemporary. Outer surface 31 of outer shell 30 preferably conforms to theshape of the intervertebral disc space 20, being in contact with annulusfibrosis 5, and may completely surround elastic body 15 as seen in FIGS.1 and 2, although outer shell 30 may only partially surround elasticbody 15. As an example, upper, lower and/or lateral voids surroundingelastic body 15 may be filled in by outer shell 30, as long as theelastic body is in some way anchored, or otherwise fixed in place, bythe outer shell so as to prevent its expulsion from, or excessivemigration in, the disc cavity. Thus, outer shell 30 may be configured tofill the aforementioned voids. Additionally, inner surface 32 of outershell 30 preferably conforms to the shape of elastic body 15, andpreferably bonds to outer surface 16 of elastic body 15 as discussedbelow. In preferred embodiments, the elastic core and the outer shellsubstantially fill the disc cavity as further discussed below.

[0041] Outer shell 30 not only provides for a properly fit implant 10within intervertebral disc space 20 for maximum load-bearing, stresstransfer, and bonding of the implant surface to the surrounding disctissues for fixation against excessive migration, it also seals anannular defect 18 for further resistance to migration and/or expulsionof the implant. Such sealing of the annular defect may also provideadditional physical and mechanical support to the disc. Furthermore, theinjectable outer shell material may provide intra-operative flexibilityin fitting the core elastic body of implant 10 within the disc space asit may compensate for the differences in geometry and size between thedisc space and the pre-formed core.

[0042] Outer shell 30 is preferably resorbable and, in such form, ispreferably replaced with tissue, such as fibrous tissue and includingfibrous scar tissue, that may aid in permanently confining the loadbearing elastic body within the disc space. Referring now to FIGS. 3 and4, tissue 33 has replaced outer shell 30, and thus surrounds elasticbody 15. Although elastic body 15 may be confined within the disc spacewith the aid of tissue 33, body 15 is expected to have some mobility fornormal biomechanics.

[0043] The dimensions of load bearing elastic body 15 may vary dependingon the particular case, but elastic body 15 is typically sized forintroduction into an intervertebral disc space. Moreover, elastic body15 is preferably wide enough to support adjacent vertebrae and is of aheight sufficient to separate the adjacent vertebrae. In order toprovide long-term mechanical support to the intervertebral disc, thevolume of elastic body 15 in the disc space should be at least about50%, preferably at least about 70%, further preferably at least about80% and more preferably at least about 90% of the volume of the entiredisc space, the remaining volume occupied by outer shell 30. However,the volume of elastic body 15 may be as large as about 99% of the volumeof the intervertebral disc space, and thus about 99% of the volume ofimplant 10. Accordingly, the volume of outer shell 30 may be at leastabout 1% of the volume of the implant, but may range from about 1% toabout 50%. The appropriate size of implant 10 desired in a particularcase may be determined by distracting the disc space to a desired levelafter the desired portion of the natural nucleus pulposus and any freedisc fragments are removed, and measuring the volume of the distractedspace with an injectable saline balloon. The disc volume can also bemeasured directly by first filling the disc space with a known amount ofthe outer shell precursor material.

[0044] Elastic body 15 may be fabricated in a wide variety of shapes asdesired, as long as the body can withstand spinal loads and other spinalstresses. The non-degradable and preformed elastic body 15 may beshaped, for example, as a cylinder, or a rectangular block. The body mayfurther be annular-shaped. For example, implant 10′ in FIGS. 12 and 13has a spiral, or otherwise coiled, shape. The implant includes a firstend 23 and a second end 24. Elastic body 15 may also be shaped togenerally conform to the shape of the natural nucleus pulposus, or maybe shaped as further described below. Although elastic body 15 is shownas one piece in, for example, FIGS. 1-4, it may be made from one orseveral pieces.

[0045] Elastic body 15 may be formed for a wide variety of biocompatiblepolymeric materials, including elastic materials, such as elastomericmaterials, hydrogels or other hydrophilic polymers, or compositesthereof. Suitable elastomers include silicone, polyurethane, copolymersof silicone and polyurethane, polyolefins, such as polyisobutylene andpolyisoprene, neoprene, nitrile, vulcanized rubber and combinationsthereof. The vulcanized rubber described herein may be produced, forexample, by a vulcanization process utilizing a copolymer produced asdescribed, for example, in U.S. Pat. No. 5,245,098 to Summers et al.from 1-hexene and 5-methyl-1,4-hexadiene. Suitable hydrogels includenatural hydrogels, and those formed from polyvinyl alcohol, acrylamidessuch as polyacrylic acid and poly(acrylonitrile-acrylic acid),polyurethanes, polyethylene glycol, poly(N-vinyl-2-pyrrolidone),acrylates such as poly(2-hydroxy ethyl methacrylate) and copolymers ofacrylates with N-vinyl pyrrolidone, N-vinyl lactams, acrylamide,polyurethanes and polyacrylonitrile, or may be other similar materialsthat form a hydrogel. The hydrogel materials may further be cross-linkedto provide further strength to the implant. Examples of polyurethanesinclude thermoplastic polyurethanes, aliphatic polyurethanes, segmentedpolyurethanes, hydrophilic polyurethanes, polyether-urethane,polycarbonate-urethane and silicone polyetherurethane. Other suitablehydrophilic polymers include naturally-occurring materials such asglucomannan gel, hyaluronic acid, polysaccharides, such as cross-linkedcarboxyl-containing polysaccharides, and combinations thereof. Thenature of the materials employed to form the elastic body should beselected so the formed implants have sufficient load bearing capacity.In preferred embodiments, a compressive strength of at least about 0.1Mpa is desired, although compressive strengths in the range of about 1Mpa to about 20 Mpa are more preferred.

[0046] Outer shell 30 may be formed from a wide variety ofbiocompatible, preferably elastic, elastomeric or deformable natural orsynthetic materials, especially materials that are compatible withelastic body 15. The outer shell materials preferably remain in anuncured, deformable, or otherwise configurable state during positioningof the elastic body in the interverterbral disc space, and shouldpreferably rapidly cure, become harder or preferably solidify afterbeing introduced into the intervertebral disc space, or, in otherembodiments, prior to positioning of the elastic body in theintervertebral disc space. In preferred embodiments, the outer shellmaterials may remain deformable after they harden or otherwise solidify.Suitable materials that may be used to form the outer shell includetissue sealants or adhesives made from natural or synthetic materials,including, for example, fibrin, albumin, collagen, elastin, silk andother proteins, polyethylene oxide, cyanoacrylate, polylactic acid,polyglycolic acid, polypropylene fumarate, tyrosine-based polycarbonateand combinations thereof. Other suitable materials include demineralizedbone matrix. These precursor materials may be supplied in liquid,solution or solid form, including gel form.

[0047] Elastic body 15 may include a variety of surface features onouter surface 16, including chemical modifications and surfaceconfigurations, to provide surface features that advantageously improvethe bonding between outer surface 16 of the elastic body and innersurface 32 of outer shell 30. In one form of the invention, outersurface 16 is chemically modified utilizing, for example, chemicalgroups that are compatible with the materials used to form outer shell30. Suitable chemical modifications include, for example, surfacegrafting of reactive functional groups, including hydroxyl, amino,carboxyl and organofunctional silane groups. The groups may be graftedby methods known to the skilled artisan. Other modifications includepre-coating with a primer, preferably one that is compatible with theouter shell material, such as a layer of adhesive, sealing or othermaterials used for forming the outer shell described above.

[0048] In yet another form of the invention, elastic body 15 may includea wide variety of surface configurations, such as macro-surfacepatterns, or protuberances, as seen in FIGS. 14A-14J, showing side viewsor top views of top portions of elastic bodies with various surfacefeatures. Referring now to FIGS. 14A-14J, the pattern may be a dove-tailpattern 200, a circular pattern 205, a square pattern 210, a conicalpattern 215, various wave patterns 220 and 225 and random, irregularpatterns 230. In other embodiments, a fiber 240 may be disposed inelastic body 241 and may project from the surface 242 thereof to form afibrous pattern 235. Fiber 240 may be disposed as a loop projecting fromthe surface of the elastic body, its ends may project from the surfaceof the elastic body, or the fiber may have a wide variety of otherappropriate configurations. The fiber may be a short, polymeric fiber,such as one that is cut to less than about one inch. The fiber may,alternatively, be a continuous polymeric fiber. The fiber may further bebraided, and may be woven or non-woven. The macro-surface patterns arepreferably formed during formation of elastic body 15. However, outersurface 16 of elastic body 15 may also be physically modified afterformation of elastic body 15 by, for example, laser drilling or thermaldeformation. Physical modifications include, for example, amicrotexturized surface formed by bead-blasting, plasma etching orchemical etching. Procedures for modifying various surfaces in thismanner are well known in the art.

[0049] In certain forms of the invention, the implant may include onlyelastic body 15 having one or more of the outer surface features asdescribed above, without the outer resorbable shell. The surfacefeatures are expected to provide a certain level of fixation to thesurrounding tissues for improved resistance to migration and/orexpulsion.

[0050] In yet other forms of the invention, the implant may include anelastic body that is surrounded by a supporting, or otherwiseconstraining, member wherein the supporting member is surrounded by aresorbable shell as described herein. Referring now to FIG. 5, implant400 includes a load bearing elastic body 15 that is surrounded by asupporting member 34. In one form, supporting member 34 may be apreferably flexible, peripheral supporting band that is disposedcircumferentially about elastic body 15 as seen in FIG. 5, leaving upperand lower surfaces 35 and 36, respectively, of elastic body 15 free fromthe supporting band.

[0051] As seen in FIG. 5, portions of upper and lower surfaces 35 and36, respectively, of elastic body 15 are exposed to directly contactouter shell 30. This exposure minimizes the amount of material needed toconstruct the supporting member, yet still effectively provides, forexample, lateral support. Although the amount of the upper and lowersurfaces of elastic body 15 that are exposed may vary, typically atleast about 50%, preferably at least about 70%, more preferably at leastabout 80% and most preferably at least about 90% of the surfaces areexposed.

[0052] In yet another embodiment shown in FIG. 6, nucleus pulposusimplant 500, that includes elastic body 15 as described above, isreinforced with supporting member 37, which takes the form of a jacket.The jacket preferably completely surrounds elastic body 15.

[0053] Suitable supporting members, including reinforcing outer bands,covers, or other jackets, may be formed from a wide variety ofbiocompatible polymers, metallic materials, or combination of materialsthat form a strong but flexible support to prevent excessivedeformation, including lateral (horizontal) deformation, of the coreunder increasing compressive loading. Suitable materials includenon-woven, woven, braided, or fabric materials made from polymericfibers including cellulose, polyethylene, polyester, polyvinyl alcohol,polyacrylonitrile, polyamide, polytetrafluorethylene, polyparaphenyleneterephthalamide, and combinations thereof. Other suitable materialsinclude non-reinforced or fiber-reinforced elastomers such as silicone,polyurethane, copolymers of silicone and polyurethane, polyolefins,including polyisobutylene and polyisoprene, neoprene, nitrile,vulcanized rubber, and combinations thereof. In a preferred form of theinvention, a combination, or blend, of silicone and polyurethane isused. Furthermore, the vulcanized rubber is preferably produced asdescribed above for the nucleus pulposus implants. Supporting members 34and 37 are advantageously made from a porous material, which, in thecase of an elastic body made from a hydrogel, or other hydrophilicmaterial, allows fluid circulation through the elastic core body toenhance pumping actions of the intervertebral disc. Supporting membersmay further be formed from carbon fiber yarns, ceramic fibers, metallicfibers or other similar fibers as described, for example, in U.S. Pat.No. 5,674,295.

[0054] FIGS. 7A-7D show supporting bands of various patterns, typicallymade from various braided materials (bands 25, 26 and 27), or porousmaterials (band 28), as described above. It is also understood thejackets may also be formed of such patterns. It is realized that thebraided materials may also be porous.

[0055] Supporting members 34 and 37 preferably decrease lateraldeformation, compared to deformation of an implant without thesupporting member, as desired. Supporting members 34 and/or 37 may, forexample, decrease lateral deformation by at least about 20%, preferablyat least about 40%, more preferably by at least about 60% and mostpreferably by at least about 80%. An implant, such as one that includesan elastic body, having such a supporting member will be flexible andotherwise resilient to allow the natural movements of the disc andprovides shock absorption capability at low to moderate applied stress,but will resist excessive deformation for disc height maintenance underhigh loading conditions. As described herein in the case of a lumbardisc, for example, low applied stress includes a force of about 100Newtons to about 250 Newtons moderate stress includes a force of about250 Newtons to about 700 Newtons, and high loading conditions, or highstress, includes a force of above about 700 Newtons. In preferred formsof the invention, the supporting member is flexible, in that it may befolded, or otherwise deformed, but is substantially inelastic, so thatthe implant is more fully reinforced or otherwise supported.

[0056] The elastic body may be covered by the jacket supporting member,or the band supporting member may be wrapped around the circumference ofthe elastic body. In a form of the invention wherein the elastic body isformed from a hydrogel, or similar hydrophilic material, the hydrogelmay be dehydrated a desired amount prior to being covered by the jacket,or prior to wrapping the band around the circumference of the hydrogelbody. The hydrogel elastic body may be exposed to saline outside of thebody, or may be inserted into the disc space wherein it will be exposedto body fluids in situ, and the body will absorb water and swell. Inreference to the peripheral band supporting member, the swelling orexpansion of the hydrogel elastic body in the horizontal direction iscontrolled by the amount of slack designed in the band. After thelimited allowable horizontal expansion is reached, the elastic body isforced to expand mostly in the vertical direction until reachingequilibrium swelling under the in vivo load. As the upper and lowersurfaces of the elastic body are not substantially constrained, thevertical expansion is mainly controlled by the applied stress and thebehavior of the hydrogel material.

[0057] In yet other forms of the invention, an implant reinforced with aperipheral supporting band as described above that is surrounded by aresorbable outer shell may be further reinforced with one or morestraps. The straps may be advantageous in preventing the peripheralsupporting band described herein from slipping, or otherwise sliding offthe implant. Referring now to FIGS. 8 and 9, at least one strap 420extends along upper surface 35 and at least one strap 430 extends alonglower surface 36 of elastic body 15 of implant 400. Ends 421 of strap420 and ends 431 of strap 430 are each preferably connected, orotherwise attached, to peripheral supporting band 34′. The point ofattachment may be any location that will secure the strap, including atthe upper margins 138 of the band, lower margins 139 of the band or anyregion between the upper and lower margins. Although two straps 420 and430 are shown extending along upper surface 35 and lower surface 36,respectively, in FIGS. 8 and 9, one continuous strap may be utilizedthat extends completely around the implant, or the strap utilized may bein one, two or multiple pieces, as long as the combination of straps aresufficient to prevent excessive slipping and or sliding of thesupporting band. Furthermore, more than one strap may extend along uppersurface 35 and more than one strap may extend along lower surface 36 ofelastic body 15, as seen, for example, in FIGS. 10 and 11 of implant500, wherein straps 520, 530, 540 and 550 are shown attached, orotherwise connect to supporting member 34″. It is realized that thestraps may be present in one or more pieces. For example, straps 520 and530 may form a single strap, as may straps 540 and 550, or may allcombine to form a single strap.

[0058] In other aspects of the invention, kits designed for forming theintervertebral disc nucleus pulposus implants that include the outershell described above are provided. In one form, a kit may include aload bearing elastic body as described above, along with a container ofmaterial to form the outer, preferably resorbable, shell. The materialmay be selected from the materials as described above. Moreover, thecontainer that houses the material that forms the shell may be made froma wide variety of materials that are compatible with the outer shellmaterial, including glass and plastic. The kit may further include asupporting member, such as a supporting band, jacket or other outercover as described above. Generally, the kits include sterile packagingwhich secures the kit components in spaced relation from one anothersufficient to prevent damage of the components during handling of thekit. For example, one may utilize molded plastic articles known in theart having multiple compartments, or other areas for holding the kitcomponents in spaced relation.

[0059] In a further aspect of the invention, nucleus pulposus implantsare provided having shape memory that are configured to allow extensiveshort-term manual, or other, deformation without permanent deformation,cracks, tears, breakage or other damage, that may occur, for example,during placement of the implant into an intervertebral disc space.Referring now to FIGS. 15A and 16A, in one form of the invention,implant 40 includes a load bearing elastic body 41 with shape memory andhaving a first end 42 and a second end 43 that are positioned adjacentto a central portion 44 to form at least one inner fold 45. Inner fold45 preferably defines at least one aperture 46 which is advantageouslyarcuate. The elastic body is deformable, or otherwise configurable,manually, for example, from this first folded, or otherwise relaxedconfiguration shown in FIG. 15A into a second, substantiallystraightened, or otherwise non-relaxed configuration shown in FIG. 16Afor placement into the intervertebral disc space. As elastic body 41 hasshape memory, it returns by itself, automatically, back into the firstfolded, relaxed configuration once manual or other force is no longerexerted on the body. These implants therefore provide improved handlingand manipulation characteristics in that they may be deformed,configured and otherwise handled by an individual without resulting inany breakage or other damage to the implant.

[0060] Further describing the shape memory nucleus prosthesis implant40, implant 40 includes surface depressions 47, or other surfaceirregularities as more fully described below, that form inner fold 45when the implant is in its relaxed configuration. Ends 42 and 43 haveend surfaces 42 a and 43 a, respectively, that are generally flat, andsubstantially parallel, or perpendicular in other forms, to an axis Xpassing through the width of the implant in its relaxed configuration,wherein the ends may abut each other as seen in FIGS. 15A, 15B and15E-15N. The ends of the implant may each alternatively abut the centralportion of the implant, as shown for implants 60 and 70 in FIGS. 15C and15D, respectively, to form a generally bi-lobed or binocular-shapedimplant.

[0061] Alternatively, in other forms of the invention, one end of theimplant may be tapered, or otherwise specifically shaped, and the otherend may be shaped complementary to the tapered, or otherwise shaped,end. Moreover, either one or both sides 96 a and 96 b of the ends of thenucleus pulposus implant may be tapered. For example, and as seen inFIGS. 15F and 16F, both sides of end 93 of implant 90 are tapered toform a pointed end, such as a generally V-shaped end, thatadvantageously fits into a complementary-shaped (e.g., V-shaped)depression 95 defined by end 92. An implant having only one inner foldthat defines one aperture and ends that are similarly configured as ends92 and 93 is shown in FIGS. 15J and 16J. As another example, one side ofeach of the ends of the implant maybe oppositely tapered as seen inFIGS. 15G and 16G. That is, side 108 a of end 102 of implant 100 andopposite side 109 b of end 103 are tapered as seen in FIGS. 15G and 16G.End surfaces 102 a and 102 b of implant 100 are transverse to axis Xwhen the implant is in its relaxed configuration shown in FIG. 15G. Inthose embodiments where the ends of the implants are tapered, orotherwise shaped, it is preferred that, when the ends of the implantscontact each other or the central or other portion of the implant, animplant is formed that is uniform along the length of the implantthrough the region of contact.

[0062] Although the implant may assume a wide variety of shapes, it istypically shaped, in its folded, relaxed configuration, to conform tothe shape of the natural nucleus pulposus.

[0063] In yet other forms of the invention, the folding implant may havea surface that includes surface projections that further aid in allowingshort-term deformation of the implant without permanent deformation orother damage as described above. Referring now to FIGS. 15D and 16D,implant 70 includes a load bearing elastic body 71 having a first end72, a second end 73 and a central portion 74. Inner fold 75 defines anaperture 76 and includes an inner fold surface 77 having wrinkles, orprojections 78 thereon. Projections 78 of inner fold surface 77 extendinto aperture 76. These wrinkles advantageously facilitate stretching ofthe implant without deformation, cracking, tearing, breakage, or otherdamage when the implant is straightened or elongated for insertion intothe intervertebral disc space. In the embodiment shown in FIGS. 15D and16D, the wrinkles, or surface projections, extend along the entirelength of elastic body 71, including central portion 74. Other implantshaving wrinkled inner fold surfaces are seen in FIGS. 15E and 16E andother wrinkle configurations upon folding the implant are seen in FIGS.15K-15N and 16K-16N.

[0064] In certain preferred forms of the invention, the aperturesdefined by the inner folds of the implants described above have a radiusof at least about 1 mm. Moreover, in other preferred forms of theinvention, a reinforcing material may be included at the inner foldsurface to further improve the structural integrity of the implant. Thereinforcing material may be a fabric that is either woven, or non-woven,and may be formed from braided fibers for further strength. Thereinforcing material may be positioned on the inner fold surface, mayproject therefrom or may be entirely embedded under the inner foldsurface. The implant may be formed as a single piece, or may be formedof more than one piece that is connected to the other pieces that formthe assembled implant by fabric that may be made from braided or otherfibers. Although these implants are designed to be used without ananchoring outer shell, they, as well as all of the implants describedherein, may form the core elastic body of an implant that includes theouter shell described herein.

[0065] The implants may obtain their shape memory characteristics in avariety of ways. For example, the implants may be formed in a mold intoa desired final shape, and, when deformed from this final shape byapplication of an external force, will return to the final shape uponrelease of the force.

[0066] In yet another embodiment of the invention, a nucleus pulposusimplant is provided that has a locking feature, with optional shapememory characteristics, and thus may also resist being expelled from thedisc cavity to some extent. In one form of the invention as seen inFIGS. 17-19, an implant 300 includes a load bearing elastic body 301having a first end 302 and a second end 303. The ends are typicallyconfigured for mating engagement with each other. Elastic body 301 has afirst, locked configuration wherein first end 302 and second end 303 arematingly engaged to each other as seen more particularly in FIG. 17.When elastic body 301 has shape memory characteristics, elastic body 301is deformable, manually, for example, into a second, substantiallystraightened, non-relaxed configuration for insertion into anintervertebral disc space, as seen in FIG. 19, and may automatically beconfigured or otherwise returned back into the first, locked, relaxedconfiguration after-insertion due to its shape memory characteristics.In those cases where the elastic body does not have shape memorycharacteristics and the elastic body is configurable into a lockedand/or straightened configuration, and in those cases where the elasticbody has shape memory characteristics, the elastic body may also beplaced into its locked configuration with the assistance of externalforce.

[0067] More particularly describing one form of the invention, end 302defines an internal channel 304 as seen in FIG. 19 whereas end 303 isconfigured to conform to the shape of internal channel 304. The channelmay take the form of a wide variety of shapes, as long as the ends ofthe elastic body may be matingly engaged to form a locked configuration.As seen in FIG. 19, the channel is somewhat hour-glass shaped. Manual,or other force, may be applied to end 303 so that it may be temporarilydeformed, or configured, sufficiently to pass through narrowed passage305 within internal channel 304. Once properly positioned, end 303 willbe secured within channel 304, as end edges 303 a and 303 b are bracedagainst channel edges 304 a and 304 b, respectively. Alternatively, oneend of an implant with a locking feature may be friction-fit within theinternal channel present in the other end of the implant. Thefriction-fit may arise as a result of the relative size differencesbetween the inner diameter of the channel formed by one end and theouter diameter of the other end of the implant. Additionally, and/oralternatively, the outer surface of one end, and/or the inner surface ofthe channel defined by the other end, may include surface roughenings asdescribed herein that aid in achieving the friction-fit. The implant mayalso be constructed from the biocompatible polymeric materials asdescribed above.

[0068] When the implants are formed from an elastic material, such as ahydrogel, or other similar hydrophilic material, or include theresorbable outer shell, they may advantageously deliver desiredpharmacological agents. The pharmacological agent may be a growth factorthat may advantageously repair the endplates and/or the annulusfibrosis. For example, the growth factor may include a bonemorphogenetic protein, transforming growth factory (TGF-β), insulin-likegrowth factor, platelet-derived growth factor, fibroblast growth factoror other similar growth factor or combination thereof having the abilityto repair the endplates and/or the annulus fibrosis of an intervertebraldisc.

[0069] The growth factors are typically included in the implants intherapeutically effective amounts. For example, the growth factors maybe included in the implants in amounts effective in repairing anintervertebral disc, including repairing the endplates and the annulusfibrosis. Such amounts will depend on the specific case, and may thus bedetermined by the skilled artisan, but such amounts may typicallyinclude less than about 1% by weight of the growth factor. The growthfactors may be purchased commercially or may be produced by methodsknown to the art. For example, the growth factors may be produced byrecombinant DNA technology, and may preferably be derived from humans.As an example, recombinant human bone morphogenetic proteins (rhBMPs),including rhBMP 2-14, and especially rhBMP-2, rhBMP-7, rhBMP-12,rhBMP-13, and heterodimers thereof may be used. However, any bonemorphogenetic protein is contemplated including bone morphogeneticproteins designated as BMP-1 through BMP-18.

[0070] BMPs are available from Genetics Institute, Inc., Cambridge,Mass. and may also be prepared by one skilled in the art as described inU.S. Pat. No. 5,187,076 to Wozney et al.; U.S. Pat. No. 5,366,875 toWozney et al.; U.S. Pat. No. 4,877,864 to Wang et al.; U.S. Pat. No.5,108,922 to Wang et al.; U.S. Pat. No. 5,116,738 to Wang et al.; U.S.Pat. No. 5,013,649 to Wang et al.; U.S. Pat. No. 5,106,748 to Wozney etal.; and PCT Patent Nos. WO93/00432 to Wozney et al.; WO94/26893 toCeleste et al.; and WO94/26892 to Celeste et al. All bone morphogenicproteins are contemplated whether obtained as above or isolated frombone. Methods for isolating bone morphogenetic protein from bone aredescribed, for example, in U.S. Pat. No. 4,294,753 to Urist and Urist etal., 81 PNAS 371,1984.

[0071] In other forms of the invention, the pharmacological agent may beone used for treating various spinal conditions, including degenerativedisc disease, spinal arthritis, spinal infection, spinal tumor andosteoporosis. Such agents include antibiotics, analgesics,anti-inflammatory drugs, including steroids, and combinations thereof.Other such agents are well known to the skilled artisan. These agentsare also used in therapeutically effective amounts. Such amounts may bedetermined by the skilled artisan depending on the specific case.

[0072] The pharmacological agents are preferably dispersed within thehydrogel, or other hydrophilic, implant for in vivo release, and/or,with respect to the implants with the resorbable outer shell, may bedispersed in the outer shell. The hydrogel can be cross-linkedchemically, physically, or by a combination thereof, in order to achievethe appropriate level of porosity to release the pharmacological agentsat a desired rate. The agents may be released upon cyclic loading, and,in the case of implants including a resorbable outer shell, uponresorption of the shell. The pharmacological agents may be dispersed inthe implants by adding the agents to the solution used to form theimplant, by soaking the formed implant in an appropriate solutioncontaining the agent, or by other appropriate methods known to theskilled artisan. In other forms of the invention, the pharmacologicalagents may be chemically or otherwise associated with the implant. Forexample, the agents may be chemically attached to the outer surface ofthe implant.

[0073] The implants described herein may have embedded therein smallmetal beads or wire for x-ray identification.

[0074] Methods of forming and implanting the nucleus pulposus implantsdescribed herein are also provided. In one form of the invention, withrespect to implant 10 described above having the anchorable outer shell30, implant 10 may be formed by first forming elastic body 15 and thenforming the outer shell. Methods of forming elastic body 15 are wellknown in the art.

[0075] For example, if the elastic body is made of elastomericmaterials, such as powdered elastomers including, for example,styrene-ethylene/butylene block copolymers, the powdered elastomer maybe placed into an appropriate mold and may be compressed and heated tomelt the powder. The mold is then cooled to room temperature. If theelastic body is made from a hydrogel, such as a polyvinyl alcohol, thepolyvinyl alcohol powder may be mixed with a solvent, such as, forexample, water or dimethylsulfoxide, or combinations thereof, and heatedand shaken until a uniform solution is formed. The solution may then bepoured into a mold, such as a rubber mold, and may be cooled at anappropriate temperature, such as about 0° C. to about −80° C., forseveral hours to allow for crystallization. After cooling, the hydrogelcan be partially or completely hydrated by soaking and rinsing withwater but, in certain preferred embodiments, may remain dehydrated sothat it may be inserted through a smaller aperture in the annulusfibrosis.

[0076] Prior to positioning the implant in the interverterbral discspace, an incision may be made in the annulus fibrosis, or one may takeadvantage of a defect in the annulus, in order to remove the naturalnucleus pulposus and any free disc fragments within the intervertebraldisc space. The disc space is then distracted to a desired level. Onceformed, and after preparing the disc space for receiving the implant,elastic body 15 may be implanted into the intervertebral disc spaceutilizing devices well known in the art and as described in U.S. Pat.Nos. 5,800,549 and 5,716,416. If the outer shell precursor material wasalready placed in the intervertebral disc space, excess precursormaterial may flow out of the disc space. This excess material should bepromptly removed before it sets or otherwise cures. The outer shellmaterial may be injected, or otherwise introduced, into the disc spaceutilizing devices that are well known in the art, such as syringes,sealant/caulk guns, automatic liquid injectors, and applicators thatinclude, for example, two separate syringes which allow for simultaneousmixing of the components in a static mixer and delivery to the site, andmay be injected either prior to or after introduction of the implantinto the disc space. Whether the outer shell material is introducedprior to or after introduction of the implant into the disc space, thedistractor is then removed, any excess precursor material seeping out ofthe disc space is removed and the precursor material within the discspace is cured to form the outer shell. It is noted that the elasticbody may already be surrounded by the outer shell, which may be in apartially or fully hardened state but preferably remains deformable,prior to introducing the elastic body into the intervertebral discspace.

[0077] In yet another form of the invention, a method for implanting aprosthetic intervertebral disc having shape memory is provided. In oneembodiment, an implant including a load bearing elastic body having afirst end and a second end positioned adjacent to a central portion toform at least one inner fold as described above is provided. The implant40, for example, may be deformed by, for example, manual force into asubstantially straightened, non-relaxed configuration for insertionthrough an aperture formed in the annular fibrosis as indicated in FIG.20, and as best seen in FIG. 21. The aperture may be formed throughdeterioration or other injury to the annulus fibrosis, or may be made bypurposely incising the annulus. The implant may then be positioned in adelivery tool 310 known in the art, such as that described in U.S. Pat.No. 5,716,416, and inserted through aperture 18 in annulus 19. As theimplant enters the intervertebral space 20 and is no longer subject tomanual force, it deforms back into its relaxed, folded configuration asseen in FIG. 21. A portion, or substantially all, of the natural nucleuspulposus may be removed from the intervertebral disc space, depending onthe circumstances, prior to introduction of the implant into theintervertebral disc space. When implanting an implant that includes alocking feature, or other implant with shape memory as described herein,a similar protocol is followed. Additionally, with respect to an implantwith a locking feature, the implant may be placed into the lockedconfiguration with external force, imposed by, for example, medicalpersonnel.

[0078] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrative and not restrictive in character, it being understoodthat only the preferred embodiment has been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected. In addition, all references citedherein are indicative of the level of skill in the art and are herebyincorporated by reference in their entirety.

What is claimed is:
 1. An intervertebral disc nucleus pulposus implant,comprising: a load bearing elastic body sized for introduction into anintervertebral disc space, said body surrounded by a resorbable shell.2. The implant of claim 1, wherein said resorbable shell is comprised ofan elastic material.
 3. The implant of claim 1, wherein said resorbableshell is comprised of a material selected from the group consisting offibrin, albumin, gelatin, collagen, elastin, silk, demineralized bonematrix, polyethylene oxide, polyethylene glycol, polyvinyl alcohol,polypropylene fumarate and combinations thereof.
 4. The implant of claim1, wherein said elastic body is comprised of a hydrogel material.
 5. Theimplant of claim 4, further including a pharmacological agent associatedwith said hydrogel material, said resorbable shell, or a combinationthereof, said agent selected from the group consisting of growthfactors, anti-inflammatory drugs, antibiotics, analgesics, andcombinations thereof.
 6. The implant of claim 5, wherein saidpharmacological agent is a growth factor.
 7. The implant of claim 6,wherein said growth factor is selected from the group consisting oftransforming growth factor β, bone morphogenetic proteins, fibroblastgrowth factors, platelet-derived growth factors, insulin-like growthfactors and combinations thereof.
 8. The implant of claim 7, whereinsaid growth factor is a recombinant human protein.
 9. The implant ofclaim 1, wherein said elastic body is comprised of a polymer selectedfrom the group consisting of elastomers and hydrogels.
 10. The implantof claim 1, wherein the outer surface of said elastic body includesprojections extending therefrom, said projections configured forenhancing fixation of said body in said intervertebral space.
 11. Theimplant of claim 10, wherein said projections comprise fiber loops. 12.The implant of claim 1, wherein the outer surface of said elastic bodyis microtexturized.
 13. The implant of claim 12, wherein saidmicrotexturizing is performed by a process selected from the groupconsisting of bead blasting, plasma etching, chemical etching andcombinations thereof.
 14. The implant of claim 1, wherein the outersurface of said elastic body includes reactive chemical groups selectedfrom the group consisting of hydroxyl groups, amino groups, carboxylgroups and organofunctional silane groups, said groups enhancingfixation of said elastic body to said resorbable shell.
 15. The implantof claim 1, wherein said resorbable shell is formed in-situ.
 16. Anintervertebral disc nucleus pulposus implant, comprising: a load bearingelastic body of hydrogel material sized for introduction into anintervertebral disc space, said body surrounded by a resorbable shell.17. An intervertebral disc nucleus pulposus implant, comprising: a loadbearing elastic body sized for introduction into an intervertebral discspace, said body surrounded by a supporting member, said supportingmember surrounded by a resorbable shell.
 18. The implant of claim 17,wherein said resorbable shell is comprised of an elastic material. 19.The implant of claim 17, wherein said resorbable shell is comprised of amaterial selected from the group consisting of fibrin, albumin, gelatin,collagen, elastin, silk, demineralized bone matrix, polyethylene oxide,polyethylene glycol, polyvinyl alcohol, polypropylene fumarate andcombinations thereof.
 20. The implant of claim 17, wherein said elasticbody is comprised of a hydrogel material.
 21. The implant of claim 17,wherein said supporting member is comprised of a supporting band. 22.The implant of claim 17, wherein said supporting member is comprised ofa jacket.
 23. An intervertebral disc nucleus pulposus implant,comprising: a load bearing elastic body sized for placement into anintervertebral disc space, said body having a first end, a second end, acentral portion, and a first configuration wherein said first end andsaid second end are positioned adjacent to said central portion to format least one inner fold, said elastic body configurable into a second,straightened configuration for insertion through an opening in anintervertebral disc annulus fibrosis, said body configurable back intosaid first configuration after said insertion.
 24. The implant of claim23, wherein said inner fold defines an aperture.
 25. The implant ofclaim 23, wherein said elastic body is comprised of a hydrogel material.26. The implant of claim 23, wherein said elastic body is comprised ofan elastomer.
 27. The implant of claim 26, wherein said elastomer isselected from the group consisting of silicone, polyurethane, copolymersof silicone and polyurethane, polyolefins, nitrile and combinationsthereof.
 28. The implant of claim 24, wherein said inner fold has asurface with projections, said projections extending into said aperture.29. The implant of claim 23, wherein said elastic body has an outersurface, said outer surface having projections extending therefrom, saidprojections configured for enhancing fixation of said body in saidintervertebral disc space.
 30. The implant of claim 23, wherein theouter surface of said elastic body is microtexturized.
 31. The implantof claim 30, wherein said microtexturizing is performed by a processselected from the group consisting of bead blasting, plasma etching,chemical etching and combinations thereof.
 32. The implant of claim 23,wherein said body further comprises a reinforcing material at said innerfold surface.
 33. The implant of claim 32, wherein said reinforcingmaterial comprises fibers.
 34. The implant of claim 23, wherein saidelastic body is comprised of a hydrogel material, said material havingat least one growth factor dispersed therein.
 35. The implant of claim34, wherein said growth factor is selected from the group consisting oftransforming growth factor β, bone morphogenetic proteins, fibroblastgrowth factors, platelet-derived growth factors, insulin-like growthfactors and combinations thereof.
 36. The implant of claim 34, whereinsaid growth factor comprises a recombinant protein.
 37. The implant ofclaim 36, wherein said recombinant protein is a human protein.
 38. Anintervertebral disc nucleus pulposus implant, comprising: a load bearingelastic body sized for placement into an intervertebral disc space, saidbody having a first end and a second end, said first end and said secondend configured for mating engagement with each other, said elastic bodyhaving a first configuration wherein said first end and said second endare matingly engaged to each other, said elastic body configurable intoa second, straightened configuration for insertion through an opening inan intervertebral disc annulus fibrosis, said body configurable backinto said first configuration after said insertion.
 39. The implant ofclaim 38, wherein one of said ends defines an internal channel, saidother end interlockingly disposed within said channel.
 40. The implantof claim 39, wherein said other end is configured to conform to theshape of said internal channel.
 41. The implant of claim 38, whereinsaid elastic body is annular-shaped.
 42. The implant of claim 38,wherein said elastic body is comprised of a hydrogel material, saidmaterial having a growth factor dispersed therein.
 43. The implant ofclaim 42, wherein said growth factor is selected from the groupconsisting of transforming growth factor β, bone morphogenetic proteins,fibroblast growth factors, platelet-derived growth factors, insulin-likegrowth factors and combinations thereof.
 44. A kit for forming anintervertebral disc nucleus pulposus implant, comprising a load bearingelastic body sized for introduction into an intervertebral disc spaceand a container of material to form a resorbable shell around said body.45. The kit of claim 44, wherein said material is curable.
 46. The kitof claim 44, wherein said resorbable shell is comprised of an elasticmaterial.
 47. The kit of claim 44, wherein said resorbable shell iscomprised of a material selected from the group consisting of fibrin,albumin, gelatin, collagen, elastin, silk, demineralized bone matrix,polyethylene oxide, polyethylene glycol, polyvinyl alcohol,polypropylene fumarate and combinations thereof.
 48. The kit of claim44, wherein said elastic body is comprised of a hydrogel material. 49.The kit of claim 44, wherein said elastic body is comprised of a polymerselected from the group consisting of elastomers and hydrogels.
 50. Akit for forming an intervertebral disc nucleus pulposus implant,comprising a load bearing elastic body sized for introduction into anintervertebral disc space, a supporting member to surround said body anda container of material to form a resorbable shell around saidsupporting member.
 51. A method for implanting an intervertebral discnucleus pulposus implant in an intervertebral disc space, comprising:(a) preparing said intervertebal disc space to receive said implant; and(b) introducing a load bearing elastic body into said disc space, saidbody surrounded in said disc space by a resorbable shell.
 52. The methodof claim 51, comprising introducing said resorbable shell into saidintervertebral disc space prior to introducing said elastic body intosaid intervertebral disc space.
 53. The method of claim 51, comprisingintroducing said resorbable shell into said intervertebral disc spaceafter introducing said elastic body into said intervertebral disc space.54. The method of claim 51, comprising introducing said resorbable shellinto said intervertebral disc space at the same time as introducing saidelastic body into said intervertebral disc space.
 55. The method ofclaim 51, comprising surrounding said elastic body with said resorbableshell prior to introducing said elastic body into said disc space. 56.The method of claim 51, wherein said resorbable shell is formed from aresorbable material in an uncured state and is cured to form said outershell.
 57. A method for implanting an intervertebral disc nucleuspulposus implant in an intervertebral disc space, comprising: (a)preparing said intervertebal disc space to receive said implant; and (b)introducing a load bearing elastic body into said disc space, said bodysurrounded by a supporting member, said supporting member surrounded insaid disc space by a resorbable shell.
 58. The implant of claim 57,wherein said supporting member is comprised of a supporting band. 59.The implant of claim 57, wherein said supporting member is comprised ofa jacket.
 60. A method for implanting an intervertebral disc nucleuspulposus implant in an intervertebral disc space, comprising: (a)providing a load bearing elastic body sized for placement into anintervertebral disc space, said body having a first end, a second end, acentral portion, and a first configuration wherein said first end andsaid second end are positioned adjacent to said central portion to format least one inner fold, said elastic body configurable into a second,straightened configuration for insertion through an opening in saidannulus fibrosis, said body configurable back into said firstconfiguration after said insertion; (b) preparing said intervertebaldisc space to receive said body; and (c) positioning said body into saidintervertebral disc space after said preparing step.
 61. The method ofclaim 60, wherein said method further comprises configuring said body atleast partially into said second, straightened configuration prior tosaid placing step.
 62. A method for implanting an intervertebral discnucleus pulposus implant in an intervertebral disc space, comprising:(a) providing a load bearing elastic body sized for placement into anintervertebral disc space, said body having a first end and a secondend, said first end and said second end configured for mating engagementwith each other, said elastic body having a first configuration whereinsaid first end and said second end are matingly engaged to each other,said elastic body configurable into a second, straightened configurationfor insertion through an opening in an intervertebral disc annulusfibrosis, said body configurable back into said first configurationafter said insertion; (b) preparing said intervertebal disc space toreceive said body; (c) positioning said body into said intervertebraldisc space after said preparing step.